Variable inductance device



Aug. 16, 1966 T. L. CRAIGE 3,267,400

VARIABLE INDUCTANCE DEVICE Filed Sept. 19, 1963 2 Sheets-Sheet 1 FIG. I.FIG. 2.

FIG. 4

INVENTOR.

THEODORE L. CWA/GE' Aug. 16, 1966 Filed Sept. 19, 1963 T. L. CRAIGEVARIABLE INDUCTANCE DEVI CE 2 Sheets-Sheet 2 I! lie I if a/v /fi 2&

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F I INVENTOR.

THEODORE Z. CPO/6E Amt/U14 QTTOQNEYI r 3,2514% 1C6 Patented August 16,1966 3,267,460 VARIABLE INDUCTANCE DEVICE Theodore L. Craige, RoslynHeights, N.Y., assignor to United Transformer Corporation, New York,N.Y., a corporation of New York Filed Sept. 19, 1963, Ser. No. 310,079 6Claims. (Cl. 336-134) the like usually include cores of magneticmaterial, with such cores being made up of plural laminations of variousconfigurations. The core sections, with laminations which may beE-shaped, C-shaped, F-shaped and the like, are assembled to form amagnetic circuit having one or more air gaps therein. By adjusting thelength of the air gap, there is provided a convenient means forcontrolling the reluctance of the magnetic core and the correspondingimpedance of the inductive device.

Various techniques have been suggested in the prior art for providing amagnetic core with a variable air gap, including the constructionsillustrated in US. Patent No. 2,879,489 of March 24, 1959, which isassigned to the assignee of the instant application. In said patent, thecore sections of the magnetic core are arranged to include a fixed coresection and a movable core section, with the core sections beingretained in a relatively fixed position in relation to each other by oneor more resilient clips which generate sufficient frictional holdingforces to maintain the relatively fixed position despite shock,vibration, temperature variations or other environmental changes. Thecompressive frictional forces afforded by the interengaged core sectionsare sufiiciently weak to enable relative motion of the movable coresection with respect to the fixed core section, for example, in responseto actuation by a screw or the like which is capable of developing asufficient actuating force to overcome the frictional forces therebypermitting adjustment of the length of the air gap. Although thisconstruction represents a notable advance in the art and has achievedwidespread commercial acceptance, there is still present the risk thathigh order shock or vibrational forces may cause some relative movementbetween the core sections and a corresponding change in the length ofthe air gap and the reluctance of the magnetic circuit. Even theslightest relative movements between the core sections will manifestthemselves as relatively large changes in the reluctance of the magneticcircuit.

Although numerous applications require the ability to achieve largeadjustments in the reluctance of the magnetic circuit and acorresponding wide range and adjustment of the inductance, there arealso many applications which require a relatively narrow range ofadjustment, in the order of 5 to 10% of the nominal value of theparticular inductive device. For such applications, it is not necessaryto provide a broad range of adjustment in the gap length, it beingsufficient to have a narrow range of adjustment which would inherentlylimit the extent of variations in inductance inadvertently introduced byenvironmental changes including vibration, shock and temperaturevariations.- There exists a need for a magnetic core for usein inductivedevices which aifords a relatively fixed gap length which cannot vary asa result of shock, vibration, temperature changes or the like, withprovision for a fine or vernier adjustment of the gap length producing acorresponding adjustment in the total inductance of the ultimateinductive device.

Broadly, it is an object of the present invention to provide a magneticcore which realizes one or more of the aforesaid objectives.Specifically, it is within the contemplation of the present invention toprovide a magnetic circuit in which provision is made for establishingan air gap having a major segment which is of relatively fixed lengthand a minor segment which is of variable length such that the overalltotal effective length of the air gap may be adjusted to bring aboutcorresponding changes in the reluctance of the magnetic circuit and ofthe inductance of the ultimate device.

In accordance with an illustrative embodiment demonstrating objects andfeatures of the present invention, there is provided a magnetic corewhich comprises plural laminations providing a magnetic circuit. Thelaminations are arranged relative to each other to define an air gap ina magnetic circuit. Provision is made for mounting at least onelamination for movement toward and away from an opposed lamination topermit adjustment in the effective length of the air gap therebyproviding for adjustrnent of total reluctance of the magnetic circuitand inductance of the actual device.

As a further feature of the invention, provision may be made in thefirst instance for mounting one of two core sections for movementrelative to the other of the core sections such that a course adjustmentmay be made in the length of the air gap, with the fine or vernieradjustment being made by provision for adjusting at least one laminationof one of the core sections in a plane parallel to the other laminationsthereof and lengthwise of the air gap such that a minor segment of theair gap is of adjustable length to permit corresponding adjustment ofthe reluctance of the magnetic core.

The above brief description, as well as further objects, features andadvantages of the present invention will be more fully appreciated byreference to the following detailed description of several presentlypreferred, but nonetheless illustrative embodiments in accordance withthe present invention, when taken in conjunction with the accompanyingdrawings, wherein:

FIG. 1 is a front elevational view, with parts broken away andsectioned, of a variable inductor embodying features of the presentinvention;

FIG. 2 is a side elevational view taken from the right of FIG. 1;

FIG. 3 is a perspective view, showing plural pairs of F-shapedlaminations of the type which may be employed in making up thetwo-section magnetic core employed in the variable inductor shown inFIGS. 1 and 2, the laminations being shown in spaced relation by pairs;

FIG. 4 is a perspective view similar to FIG. 3, but showing thelaminations in assembled relation;

FIG. 5 is a perspective showing, with parts broken away, of the magneticcore embodied in the variable inductor shown in FIGS. 1 and 2;

FIG. 6 is a sectional view taken substantially along the line 6-6 ofFIG. 5 and looking in the direction of the arrows;

FIG. 7 is a front elevational view, with parts broken away and sectionedfor the purposes of clarity, showing a modified form of variableinductor embodying further features of the present invention;

FIG. 8 is a sectional view taken substantially along the line of 88 ofFIG. 7 and looking in the direction of the arrows; and,

FIG. 9 is a top plan view, with parts broken away and sectioned to showthe top of the magnetic core embodied in the device shown in FIGS. 7 and8.

Referring now specifically to the drawings, and in particular to FIGS. 1through 6 inclusive, there is shown an adjustable inductor, generallydesignated by the reference numeral 10, embodying features of thepresent ,segment of an air gap 38 therebetween.

invention which is of the type useful for diverse low and high frequencyapplications including audio and radio frequencies. Although theinvention will be described in connection with this typical adjustableinductance device which is herein illustrated as incorporating a corehaving essentially F-shaped laminations, it will be appreciated that theinvention finds applications in diverse types of inductive devicesincorporating a magnetic core or circuit having one or more air gapstherein.

Specifically, the adjustable inductor includes a casing 12 having a base14 and a cover 16. The cover 16 is secured to the upstanding flange 14aof the base 14 by soldering 18 or the like about the margins thereof toprovide a hermetically sealed unit.

Disposed within the two-part casing 12 is the magnetic core 20 whichbasically includes two sections 22, 24, each made up of plurallaminations.

In this illustrative embodiment, the core section 22 includes aplurality of F- shaped laminations, three of which have been designatedby the reference numerals 26, 28 and 30 in FIGS. 3 and 4. In FIG. 3,alternate laminations,-such as the laminations 26, 30 are seen to bearranged one behind the other and in coextensive relation, while theintermediate laminations, such as the lamination 28 being turned 180into opposed relation. In a similar fashion, alternate laminations, suchas the laminations 32, 36 of the other core section 24 are arranged incoextensive relation, while the intermediate lamination 34 is likewiseturned 180 and end for end into opposed relation. As may be appreciatedby progressively comparing FIGS. 3 and 4, when the respectivelaminationsare assembled, successive pairs of laminations of the core sections 22,24, such as the laminations 28, 34 are disposed in coplanar relation andform one element of the core 20. Specifically, the F- shaped laminations28, 34 include outer legs 28a, 34a, inner or intermediate legs 28b, 34b,and connecting legs 28c, 34c. The intermediate or inner legs 28b, 34bare disposed centrally of the planar core element and extend toward eachother and terminate in coextensive and confronting faces which cooperateto define an elemental In similar fashion, successive pairs oflaminations of the core sections 22, 24, such as the laminations 30, 36cooperate to form further planar elements of the core which, whenstacked,

provide further elementallsegments of the air gap 38.

It will be appreciated that other standard types of laminations may beemployed in the practice of the present invention, including E-shapedlaminations of the type illustrated in the several illustrativeembodiments of the above-identified patent. Further, in lieu ofinterleaving by ones as illustrated in the drawings and as describedherein, it is obvious that the core laminations can be interleaved bygroups of more than one to reduce the cost of laminating.

Referring now to FIGS. 1, 2 and 5, it will be seen that the. magneticcore 20, when finally assembled, provides a closed magnetic-circuit orloop including the air gap 38. Specifically, the magnetic core 20includes outer legs 20a, 20b composed of alternate and interleaved legsof the respective core sections 22, 24, upper and lower legs 20c, 20d,likewise composed of alternately interleaved legs of the respective coresections 22, 24, and inner legs 20e, 20 which project upwardly anddownwardly from the lower and upper legs 20c, 20d respectively andcooperate to form the air gap 38 medially of the magnetic core 20.

The laminations (i.e. 26, 28 and 30 shown in FIG. 3) of the core section22 are secured together in stacked relation by U-shaped channel 40 whichstraddles the underside of the lower leg 20c and embraces the oppositefaces thereof. The channel 40 is secured to the laminations by ananchoring member 42 which extends through aligned apertures formed inthe connecting legs of the laminations, such as the aperture 28e shownin FIGS. 3 and 4. The anchoring member 42 may be in the form of a rivetor cold-rolled steel pin while the U-shaped channel may be secured tothe base 14 as by spot welding or the like.

Frictional interengagement between the stacked laminations is achievedby the provision of U-shaped spring clips, 44, 46 which are embracedabout respective outer legs 20a, 20b of the magnetic core 20, as seenbest in FIGS. 1 and 2. The clips 44, 46 contribute to the compressivefrictional forces between the interleaved laminations which preventdisplacement of the laminations relative to each other in response tovariations in environmental conditions including shock, vibration,temperature changes and the like.

In this illustrative embodiment, one or more laminations of the coresection 24 are mounted for movement relative to the other laminations ofsuch core section such that a corresponding small segment of the air gap38 may be adjusted in length which in turn changes the average effectivelength of the air gap 38 to bring about a corresponding variation in thereluctance of the magnetic circuit and in the resultant inductance ofthe ultimate device. Specifically, three laminations (which correspondto those designated by the reference numerals 32, 34 and 36 in FIG. 3)are secured together for movement in planes parallel to the remaininglaminations and lengthwise of the air gap 38 such that a minor segmentof the air gap, designated by the reference numeral 38b, may be adjustedin relation to the major segment 38a of the gap which is defined by theremaining laminations of the to facilitate riveting of the adjustablelaminations to the clamp 48. The clamp 48 is secured to an upwardlydirected post 52 which in turn carries an externally threaded bolt 54engaged within a depending internally threaded boss 56 having a slottedadjusting head 58. The boss 56 extends through a centrally disposedopening formed in the upper wall of the cover 16 of the casing 12 and isretainedtherein for rotation and against axial displacement by theprovision of a spacer element or Washer 60 and a locking element or ring62 which is received within an annular peripheral groove 56a formed onthe outer surface of the depending boss 56. Upon turning of the slottedadjusting head 58, there is a corresponding axial displacement of thethreaded bolt 54, serving as a lead screw, and a movement of theadjustable or floating laminations 32, 34, 36 to bring about acorresponding change in the length of the minor or adjustable'segment38b of the air gap 38.

The intermediate or central legs 20c, 20 of the mag- .netic core 20support a bobbin 64 having one or more coils 66 wound thereon. As seenbest in FIG. 2, the coil terminals, for example the coil end 6611, isconnected to a spade lug 68 which is mounted by an insulating grommet 70on the base 14 of the casing 12, a similar spade lug being provided atthe diametrically opposite corner of the base 14. Appropriatechassis-mounting bolts 72 are secured to the base 1.4 of the casing 12to faciliate the mounting of the component in its operationalenvironment. k p

In actual use, rotation of the slotted adjusting head 58 in onedirection or the other serves to translate the'lead screw 54 relative tothe internally threaded boss 56 and moves the one or more adjustablelaminations in planes parallel to the remaining laminations and in thelength direction of the adjustablesegment38b of the air gap 38.

Throughout such motion, the laminations remain in overlapping andfrictional engagement with each other, such that substantially theentire reluctance variations of the core are derived from the adjustmentof the air gap. Once an adjustment has been effected, the pressureexerted by the resilient clips 44, 46 locks the laminations againstfurther translation until an actuating force is developed whichovercomes the static frictional forces. Since only a small segment orportion of the air gap is capable of adjustment, it will be appreciatedthat excessiVe shock or vibration which would tend to displace themovable laminations can only effect correspondingly small variations inthe reluctance of the magnetic core.

Referring now to FIGS. 7 to 9 inclusive, there is shown a furtherembodiment of the present invention wherein provision is made for bothmounting one of the two core sections for movement relative to the otherof the core sections such that a gross adjustment may be made in thelength of the air gap and for making a fine or vernier adjustment. Sincemany of the structural details of this further embodiment are similar tothe embodiment shown in FIGS. 1 through 6, reference numerals have beenselected as part of a 100 series to identify corresponding parts.

The adjustable inductor 110 includes a casing 112 having a base 114 anda cover 116. The cover 116 is secured to the upstanding flange 114a ofthe base 114 by soldering 118 about the margins thereof to provide ahermetically sealed unit. Disposed within the casing 112 is the magneticcore 120 which includes two core sections 122, 124 made up of pluralF-shaped laminations arranged in the manner previously described. Thealternatively directed laminations of the lower core section 122 aresecured together by the U-shaped clamp 140 which embraces thelaminations and is secured thereto by a rivet or pin 142, with the bightof the clamp 140 being secured to the base 114, as by spot welding. Theupper core section 124, which is adjustable toward and away from thefixed core section 122 to permit overall or gross adjustment of the airgap 138, has the laminations thereof secured together for adjustment asa unit. This is achieved by the provision of an inverted U-shaped clamp148 which carries a rivet or pin 150 extending through all of thelaminations except for the floating or adjustable laminations, hereindesignated by the reference numerals 132, 134. As seen best in FIG. 8,the adjustable or floating laminations 132, 134 which are movable inplanes parallel to the remaining laminations of the core 120, afford ameans for adjusting a small and minor segment 138b of the overall airgap 138 which will bring about a corresponding adjustment in the averageeffective length of the air gap. The laminations 132, 134 areappropriately slotted, as indicated at 132a, 134a, to afford clearancein relation to the rivet or pin 150, with the invertedU-shaped clamp 148being appropriately configurated, as indicated at 148a, to facilitatesuch adjustment.

The adjustable laminations, 132, 134 are secured together and to acommon actuating head 174 which is engaged against an eccentric 176secured to a vernier shaft 178 which is journalled in the adjacent wallof the cover 116 of the casing 112. The vernier shaft 178 has a slottedend, as indicated in FIG. 8 and designated by the reference numeral 178a, to faciliate adjustment thereof and may be secured in any adjustedposition through the provision of a lock nut 180 threaded thereon andengaged against a washer 182. An appropriately configurated spring 184bears against the top wall of the cover 116 of the casing 112 andagainst the actuating head 174 to bias the same against the peripheralsurface of the eccentric 176 such that the rotational orientation of theeccentric 176 will determine the adjusted position for the laminations132,134.

As before, a screw type actuator including a slotted head 158 is securedto an upstanding post 152 connected 6 to the channel 148. In thisembodiment, the screw type actuator serves to adjust the entire movablecore section 124 with respect to the stationary core section 122.

The illustrative adjustable inductor is completed by the provision ofthe bobbin 164 which receives one or more coils 166 wound thereon andconnected to appropriate spade lugs 168 on the base 114 of the casing112.

From the foregoing, it will be appreciated that there has been providedin accordance with the present invention a variable inductor devicewhich comprises a core including plural laminations providing a magneticcircuit, with the laminations being arranged to define an air gap insuch magnetic circuit. A first group of laminations is disposedsubstantially in opposed relation to a second group of laminations toprovide a first and major segment for the air gap, while a third groupof laminations is disposed substantially in opposed relation to a fourthgroup of laminations to provide a second and minor segment for the airgap. Means are provided to mount one of the third and fourth group oflaminations for movement relative to the other group thereof such that afine adjustment may be made in the effective length of the air gap. As afurther feature of the invention, provision may be made in the firstinstance for moving all of the laminations which make up the air gaprelative to each other to achieve a gross adjustment in the length ofthe air gap.

A latitude of modification, change and substitution is intended in theforegoing disclosure and in some instances some features of theinvention will be employed without a corresponding use of otherfeatures. Accordingly, it is appropriate that the appended claims beconstrued broadly and in a manner consistent with the spirit and scopeof the invention herein.

What I claim is:

1. A variable inductive device comprising a core having plurallaminations providing a magnetic circuit, said laminations beingarranged relative to each other to define an air gap in said magneticcircuit, first groups of laminations being arranged in relation to eachother to provide a relatively fixed length for a first segment of saidair gap and a corresponding relatively fixed value of inductance, andmeans for mounting a second group of laminations for movement relativeto said air gap and in planes parallel to the lamina-tions of said firstgroup to provide an adjustable length for a second segment of said airgap and a corresponding variable inductance whereby vernier adjustmentmay be made in the total inductance of said device.

2. A magnetic core comprising plunal laminations, each of saidlaminations having at least one leg, said legs terminating inconfronting faces defining an air gap therebetween, means for retainingsaid laminations in rela- .tively fixed relation to each other exceptfor at least one lamination such that a major segment of said air gap isof a relatively fixed length, and means for adjusting said onelamination in a plane parallel to the other laminations and lengthwiseof said gap such that a minor segment of said air gap is of adjustablelength to permit vernier adjustment of the reluctance of said magneticcore.

3. A magnetic core comprising plural laminations each having an outerleg and an intermediate leg, said intermediate legs terminating inconfronting faces defining an air gap therebet-ween, said outer legsbeing interleaved and in frictional engagement, means for retaining saidlaminations in relatively fixed relation to each other except for atleast one lamination such that a major segment of said air gap is of arelatively fixed length, and means for adjusting said one lamination ina plane parallel to the other laminations and lengthwise of said gapsuch that a minor segment of said air gap is of adjustable length topermit vernier adjustment of the reluctance of said magnetic core.

4. A variable inductive device comprising a core ineluding first andsecond core sections each having plural laminations providing a magneticcircuit, said laminations of said first and second core sections beingparallel to each other and arranged relative to each other to define anair gap in said magnetic circuit, a first group of laminations of saidfirst core section being disposed substantially in opposed relation to afirst group of laminations of said second core section to provide afirst and major segment for said air gap, a second group of laminationsof said first core section being disposed substantially in opposedrelation to a second group of laminations of said second core section toprovide a second and minor segment for said air gap, means mounting oneof said core sections for lengthwise movement relative to the other ofsaid core sections such that a gross adjustment may be made in thelength of said air gap, and means mounting one of the second groups oflaminations for lengthwise movement relative to the other of the secondgroups of laminations such that a fine adjustment may be made in theefiective length of said air gap.

5. A magnetic core comprising two core sections each including plurallaminations, each of said core sect-ions having an outer leg and anintermediate leg, said intermediate legs of said core sectionsterminating in confronting faces defining an air gap therebetween, saidouter legs of said core sections being interleaved and in frictionalengagement with each other, means for retaining said core sections inrelatively fixed relation to each other such that a major segment ofsaid air gap is of a relatively fixed length, means for adjusting atleast one lamination of one of said core sections in a plane parallel tothe other laminations of said one core section and lengthwise of saidair gap such that a minor segment of said air gap is of adjustablelength to permit Vernier adjustment of the reluctance of said magneticcore, and fine adjusting means operatively connected to said onelamination for moving 8 the same against the reaction force provided bysaid interleaved outer legs.

6. A magnetic core comprising two core sections each including plurallaminations, each of said core sections having an outer leg and anintermediate leg, said intermediate legs of said core sectionsterminating in confronting faces defining an air gap therebetween, saidouter legs of said core sections being interleaved and in frictionalengagement with each other, means for retaining said core sections inrelatively fixed relation to each other such that a major segment ofsaid air gap is of a relatively fixed length, means mounting one of saidcore sections for movement relative to the other of said core sectionsuch that a gross adjustment may be made in the length of said air gap,gross adjusting means operatively connected to said one core section formoving the same against the reaction force provided by said interleavedouter legs, means for adjusting at least one lamination of one of saidcore sections in a plane parallel to the other laminations of said onecore section and lengthwise of said air gap such that a minor segment ofsaid air gap is of adjustable length to permit Vernier adjustment of thereluctance of said magnetic core, and fine adjusting means operativelyconnected to said one lamination for moving the same against thereaction force provided by said interleaved outer legs.

References Cited by the Examiner UNITED STATES PATENTS 3/1959 Mitchell336-134 3,154,756 10/1964 Bo-jarski 336l33 LARAMIE E. ASKIN, PrimaryExaminer.

JOHN F. BURNS, ROB-ERT K. SCHAEFER, Examiners.

C. TORRES, Assistant Examiner.

1. A VARIABLE INDUCTIVE DEVICE COMPRISING A CORE HAVING PLURALLAMINATIONS PROVIDING A MAGNETIC CIRCUIT, SAID LAMINATIONS BEINGARRANGED RELATIVE TO EACH OTHER TO DEFINE AN AIR GAP IN SAID MAGNETICCIRCUIT, FIRST GROUPS OF LAMINATIONS BEING ARRANGED IN RELATION TO EACHOTHER TO PROVIDE A RELATIVELY FIXED LENGTH FOR A FIRST SEGMENT OF SAIDAIR GAP AND A CORRESPONDING RELATIVELY FIXED VALUE OF INDUCTANCE, ANDMEANS FOR MOUNTING A SECOND GROUP OF LAMINATIONS FOR MOVEMENT RELATIVETO SAID AIR GAP AND IN PLANES PARALLEL TO THE LAMINATIONS OF SAID FIRSTGROUP TO PROVIDE AN ADJUSTABLE LENGTH FOR A SECOND SEGMENT OF SAID AIRGAP AND A CORRESPONDING VARIABLE INDUCTANCE WHEREBY VERNIER ADJUSTMENTMAY BE MADE IN THE TOTAL INDUCTANCE OF SAID DEVICE.